The invention relates generally to electrical connectors and more particularly to land grid array (LGA) connectors.
Current and future high performance computer systems and server systems rely on both large scale packaging of multiple high density interconnect modules and boards that must be upgraded in service. Many of these interconnect applications are beyond the scope of reliability using traditional solder interconnection technology as combined temperature gradients, packaging LW size and packaging mass prompt conditions for premature thermomechanical solder failure outside the scope of contact reliability requirements needed for system performance, and do not support the ability to provide field replacement of individual module elements. Thus, land grid array (LGA) connectors that provide removable and repluggable socketing capability of modules and boards are the required interconnect methodology.
LGA connectors that are used to electrically connect printed circuit boards to modules or other circuit boards provide high density, high performance interconnections that provide field upgrade and replacement capabilities. However, interfaces created between connector contacts and board surfaces are subject to potential reliability degradation from the entrance of corrosive environmental gases and particulate debris into the LGA contact areas. Of particular concern is the reliability of LGA interconnects that must be recreated because of the necessity to provide an in-service field upgrade or module replacement. As mating or separation and remating of LGA contact interfaces prompts significant potential for intermittent interconnection conditions to be created from both the presence of corrosion products or particulate debris on board and module surfaces which can create insulating layers or contact standoff conditions that inhibit reliable electrical contact formation.
To inhibit or eliminate significant potential for both corrosive gas ingress and particulate cross contamination within a land grid array (LGA) site designated for a system upgrade or required in-service module replacement, LGA connectors can be designed with in situ gaskets which seal the perimeter of the LGA contact areas of the connector to provide a barrier against particulate cross contamination and corrosive gas ingress. The gasket attaches to the frame or external walls of the LGA connector via insertion into a molded channel created within the connector frame or housing or can be affixed to the LGA frame or external connector housing using pressure sensitive adhesive films. The gasket provides interference atop card and/or module surfaces, but is sufficiently compliant such that loading of individual contacts to intended normal forces or to LGA connector frames, housings or incorporated contact standoffs is not impacted after connector actuation. These peripheral gaskets are compatible additions to frames or housings on a variety of LGA connector types including LGA connectors possessing metallic C-spring or D-spring contact members, LGA connectors comprised of wire xe2x80x9cfuzz buttonxe2x80x9d contacts, or LGA connectors possessing individual contact members comprised of metal filled polymeric elastomers.
The invention provides for significant reduction of cross contaminations by particulates and corrosive gases within an LGA connector system itself, thereby eliminating or reducing the need for secondary fixturing within the system packaging configuration, or by providing contamination reduction potential in systems where the addition of secondary fixturing to address contamination is not possible due to multiple design constraints. Moreover the use of secondary fixturing, such as gaskets or shields, on bulk printed circuit board assemblies or modules for contamination reduction creates problems when rework of individual board or module elements is required after card assembly and test, since the bulk of gasket materials are not compatible with elevated temperature operations or liquid exposure operations required for soldering and solder rework, heat sink removal operations, post solder wash, card bake, and adhesive cure operations.
Thus, removal of secondary gaskets is required prior to rework. Unfortunately, secondary gasket removal prompts a potential for organic cross contamination onto LGA pad contacts present on boards or modules as secondary gaskets are commonly affixed with adhesives that also must be removed prior to other rework operations. By providing the gasket on a disposable element, rework operations are vastly simplified and added cleanliness control for rework operations during assembly of boards and modules is also realized. In addition, by providing a gasket element on the connector itself, contamination control is also obtained in designs where room for additional shielding in secondary format is not practical.
Currently a typical LGA presents a matrix of 750 to 5000 contacts with the upper limit expected to be extended to 7500 in the near future. Since each contact in an array requires a contact force of 1 xc2xd to 4 ounces to assure that adequate electrical contact and operational reliability are achieved, the total clamping force for a 1000 LGA matrix of contacts would be from 90 to 250 pounds. The in situ gasket must have characteristics that not only seal the printed circuit board/connector interface against contamination, but must also not interfere with the even distribution of force across the matrix of contacts. The gasket material must preferably deform and seal without elasticity that would produce localized forces that disturb the equality of force applied to each contact. Preferably, the gasket material is secured to the LGA connector and deforms inelastically so that a seal is formed without introducing a restorative force that would increase the total clamping force required to achieve the minimum adequate force at each contact interface. The seal could also be effected by a deadsoft, malleable metal which possess no elasticity or memory that would tend to restore the metal to or approach an original configuration.